Dovetail joints are well known and widely used to securely interlock two pieces of wood. Historically, such joints have been widely used in the construction of furniture as well as in the manufacture of shelving, wood containers and fence structures.
A dovetail joint is formed by cutting a female dovetail-shaped groove in a piece of wood and inserting a matching male tenon at the end of a second piece of wood in the groove. A dovetail-shaped groove is a groove with the bottom of the groove wider than the top so that the two sides of the groove have opposing slants. The tenon on the second piece of wood is held in the groove by a wedging action, which forms a very strong joint. The inherent strength of such joints, provided the tenon and groove are properly cut to match, makes them a favored method in the furniture industry to join wood pieces together. Dovetail joints are also widely used in the manufactured shelving business to join supports to the shelves.
Dovetail joints are favored in the manufactured shelving business, not only because of the strength of such joints, but also because the joint can be made so it is not visible when the shelf is hung on a wall or other supporting surface. In most cases the dovetail groove is started from the shelf edge that is to be mounted against the wall. This means the tenon on the shelf support is inserted in the groove from the back edge. Because the groove is not usually cut across the entire planar surface of the shelf, the outline of the dovetail joint is not visible when the shelf is installed. This gives such shelving an attractive appearance as well as providing a strong support for relatively heavy loads. Such shelving can be made in any length and with any number of supports.
Notwithstanding the obvious benefits of using dovetail joints to construct and manufacture shelving and furniture, there are several disadvantages. One disadvantage is that a dovetail joint should be precisely sized. The joint can tolerate little or no variance between the size of the female dovetail groove and the male tenon. If the tenon is too small, the two pieces will not achieve an interference fit and may easily come apart. If the tenon is oversized, the two pieces of wood will prove difficult to join without the use of force, which force could damage the shelf by chipping or splintering the edges of the dovetail groove or the tenon. Because such precision is required, the forming and assembly of products using dovetail joints may be more expensive than using other techniques. Even if a near perfect fit of the tenon into the dovetail groove is achieved, age related shrinkage caused by drying of the wood, as well as swelling and shrinkage caused by variable humidity conditions, may cause the joint to loosen. This is why dovetail joints are typically held together by dowels or by an adhesive. Manufacturing costs are increased when a dowel is required or adhesive is used because additional raw materials are required and an additional manufacturing step to apply the adhesive or install the dowel is required.
An alternative to the use of adhesive or dowels to secure dovetail joints is to use a friction fit. That is, make the tenon slightly larger than the dovetail groove and rely on friction to hold the two pieces together. When shelving is made that relies on a friction fit to hold the pieces together, the problems of an uneven or excessive application of force to join the two pieces should be addressed. If excessive force is used, the shelving materials can be damaged by chipping or splintering the edges of the groove or tenon, thereby causing a loss of materials that adversely affects the economics of the manufacturing process. Such problems become even more pronounced if soft wood materials, such as white pine, are used.
While shelving and other like items can be manufactured by forming a dovetail groove with a router and either manually forcing an oversized tenon into the groove, to get a friction fit to hold the pieces together, or by securing the tenon in the groove with an adhesive or a dowel, such methods are not cost effective when a large number of relatively inexpensive shelves are to be manufactured. To be economically competitive, such shelving should be assembled as efficiently as possible using low cost techniques. In addition, it is critical that the manufacturing process provide a level of quality control that assures the production of a consistent product.
Accordingly, what is needed in the art is a machine that can cut a groove on the surface of a workpiece, such as piece of soft wood, and insert the tenon at the end of a second workpiece, also a piece of soft wood, into the groove on the first workpiece.